The boom has two end caps, one is the out haul casing, the other is the goose neck connecting assembly. As the foot of the sail lies across the top of the boom. The out haul is important as it allows for a flattening of the sail. Taking the "belly" out of the foot of the sail reduces performance. This is great when the winds of March howl across Beaver Lake. During the calmer months of the summer, we slack the out haul to put the "belly" in the sail, increasing draft and improving the sail's performance. Think of a sail as an airplane wing. I know, airplane wings are horizontal and sails are vertical. However, the principal is the same. The more "belly" or draft in the sail the more the sail approximates a wing. When going to weather (sailing towards the wind) the aerofoil affect is most pronounced. That is to say, that the air flowing over the sail creates a lower pressure on the outside of the sail. This essentially, pulls the boat along.
Suffice it say that the boom has not seen such tender loving care as with the exception of a bit of paint, it has likely not been off the boat in 25 years. That's 25 years of corrosion. While most of it is stainless steel, it was still corroded.